Exploring the effect of relative humidity on dynamic evolution of flax fibre's microfibril angle through in situ tensile tests under synchrotron X-ray diffraction

Tensile properties of elementary flax fibres were investigated through in situ Synchrotron X-ray diffraction in order to understand the effect of tensile loading, on the internal reorganisation of crystalline cellulose; for the first time, these experiments were conducted for different RH conditions. Synchrotron radiation experiments were considered under reduced spot size and short acquisition times to quantify the variation of cellulose microfibril angle (MFA) in a single fibre during tensile loading, while limiting the fibre damage during X-ray exposure. The acquisitions were possible at various relative humidity (RH) conditions (from 25 % to 92 %) in order to quantify the effects of different hygro-mechanical actions upon elementary flax fibres. The results show that the MFA decreases with the increase of the applied loading, indicating a partial realignment of the cellulose microfibrils with the loading axis. The MFA at fracture point shows a decrease between - 11 and - 15 % compared to the initial MFA at all relative humidity conditions studied. The strain at break of the fibres increases with increasing relative humidity. This mechanical behaviour shows the plasticizing effect of water on the non-cellulosic amorphous matrix of cell wall.

Automated summary

The tensile properties of elementary flax fibres were investigated using in situ Synchrotron X-ray diffraction. The results showed that the cellulose microfibril angle (MFA) decreased with increasing applied loading, indicating a partial realignment of the microfibrils. The MFA at fracture point decreased by 11% to 15% compared to the initial MFA. Additionally, the strain at break of the fibres increased with increasing relative humidity.